Field of the Invention
The present invention relates to display technology. More specifically, the present invention relates to digital backplanes that control light modulating elements, spatial light modulators and light sources.
Discussion of Related Art
Micro-displays typically include light modulating backplane and a light modulating unit or a light emitting unit. Light modulating units include such technologies as liquid crystal on silicon (LCOS) and digital micro mirrors devices (DMD). Light emitting units include technologies such as Organic light emitting diodes (OLED). The technology used in such micro displays can also be used to make larger display units.
FIGS. 1A and 1B illustrate a small portion of a conventional LCOS display 100. Specifically, FIG. 1B only shows 24 pixels of LCOS display 100. Generally, a LCOS display would have thousands of pixels. FIG. 1A is a cross sectional view of display 100 along the A A′ cut shown in FIG. 1B. However FIG. 1B shows only one layer of LCOS display 100.
In FIG. 1A, a substrate 110 supports pixel control circuits PCC_1_1, PCC_2_1, PCC_3_1, PCC_4_1, PCC_5_1, and PCC_6_1. Above the pixel control circuits are pixel electrodes PE_1_1, PE_2_1, PE_3_1, PE_4_1, PE_5_1, and PE_6_1. Each pixel electrode PE_X_Y is coupled to and controlled by pixel control circuit PCC_X_Y. Thus, pixel electrode PE_1_1 is coupled to and controlled by pixel control circuit PCC_1_1. Similarly, electrodes PE_2_1, PE_3_1, PE_4_1, PE_5_1, and PE_6_1 are coupled to and controlled by pixel control circuits PCC_2_1, PCC_3_1, PCC_4_1, PCC_5_1, and PCC_6_1, respectively. For LCOS display 100, the pixel electrodes are made of a reflective conductor to reflect incoming light as explained below. As shown in FIG. 1B, the polarized electrodes are arranged in a rectangular matrix. For clarity the pixel electrodes are PE_X_Y, where X refers to the column location of the pixel electrode and Y refers to the row location of the pixel electrode.
Substrate 110 would also include various, logic circuits to support the operation of the pixel control circuits. For clarity these logic circuits are omitted in the Figures because the omitted logic circuits, which are well known in the art, are not an integral aspect of the present invention. Substrate 110, the pixel control circuits, the pixel electrodes and the omitted logic circuits form the light modulating backplane. An example of a light modulating backplane is described in U.S. Pat. No. 7,071,908, entitled “Digital Backplane” by Guttag et al., which is included herein by reference. Another example of a light modulating backplane is described in U.S. Pat. No. 8,605,015 entitled “Spatial Light Modulator with Masking Comparators” by Guttag et al., which is incorporated herein by reference.
The light modulating unit of LCOS display 100 includes a liquid crystal layer 120, an alignment layer 130, a transparent common electrode layer 140, and a protective glass layer 150. Protective glass layer 150 protects the rest of LCOS display 100 but typically does not manipulate incoming or reflected light. Transparent common electrode layer 140 works with the pixel electrodes to manipulate the liquid crystals in liquid crystal layer 120. Alignment layer 130 aligns the liquid crystals in liquid crystal layer 120 to properly manipulate incoming and reflected light. Liquid crystal layer 120 contains liquid crystals that are controlled by the pixel electrodes to selectively pass incoming polarized light through liquid crystal layer 120. Specifically, when a pixel electrode is charged to an “active state” by the corresponding pixel control circuit polarized light can pass through the area of liquid crystal layer 120 above the pixel electrode and be reflected back by the pixel electrode. However, if the pixel electrode is in an inactive state polarized light is blocked in the area of liquid crystal layer 120 above the pixel electrode. Pulse width modulation is used to create different contrast levels. For color displays, color filters can be included in the light modulating unit or field sequential color schemes (i.e. rapidly cycling through three different colored light sources).
The transition from standard definition video to high definition video and beyond has created a great demand for higher resolution displays. However, for light modulating backplanes the size of the pixel control circuits is becoming a limiting factor for the density of pixels in a light modulating backplane. Thus, to create higher resolution light modulating backplanes using conventional techniques, the overall size of the light modulating backplane must be increased. However, increasing the size of the light modulating backplane would also increase the cost and power consumption. Hence there is a need for a method or system create high resolution light modulating backplanes.